Bump to core 6.4.0

[annetill]

Please check if the PR fulfills these requirements

• [X] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem?

No

What kind of change does this PR introduce?

Dependency update

What is the current behavior?

Uses powsybl-core 6.4.0-RC2.

What is the new behavior (if this is a feature change)? Uses powsybl-core 6.4.0.

Does this PR introduce a breaking change or deprecate an API?

• [ ] Yes
• [X] No

If yes, please check if the following requirements are fulfilled

• [ ] The Breaking Change or Deprecated label has been added
• [ ] The migration steps are described in the following section

What changes might users need to make in their application due to this PR? (migration steps)

Other information:

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud